1992 F150 4.9 Auto 2wd 136K
Ran great one day and next it was hard to start and unbelievably rough idle and stalled like its missing on multiple cylinders next day its fine again and put a few miles on it than few days later back to rough running and I cant figure it out. It will run in carb clean sprayed in it all day so I believe its a fuel issue.

Check fuel pressure on rail and its 48 or so while cranking and remained there when it did start (while running rough). It did blean down rather quickly when cranking stopped.
Replaced Wires and plugs. No change. Tested spark on all CYC and they all fire.
Pulled cyc 1 fuel injector plug and put on noid light and get nothing when KOEO or while cranking but same noid light on cyc 2 gets lit with KOEO and flashed on cranking.

So I checked wiring diagram and seems red wire has power to all injectors and 1,3,5 get ground signal from ECU on tan wire and 2,4,6 get ground signal from ECU on white wire. Checked all harnesses and all look on so ran wire from ECU tan to injector wire tan and tried it and same result. No light on cyc 1.

Thoughts?

 

Have you checked for codes?

 

No. I've not had much luck with OBD1 codes. Sent me down wrong path before. But guess can't hurt. I'll report back.

 

Yeah they can be a little cryptic at times, but usually the best place to start.

Did you pull the vacuum line from the fuel pressure regulator and check the pressure? Did it smell like gasoline? How soon did the pressure drop with the engine off and what was the psi?

 

Did not pull vacuum line. But I'll check that and see if regulator diagram is ruptured
The pressure bled down to nothing in seconds.

 

Isn't this also a common sign of a bad MAP sensor? They come up often as the likely culprit for this type of running.
Was it raining yesterday or the day before, by any chance? If yours is one of the type that's mounted up on the cowl/firewall area that's prone to water intrusion, the possibility goes up drastically.

Hopefully codes will point you in the right direction.

Paul

 

Not a good thing. While it might not always cause trouble, and might even not be your current issue, bleeding off pressure that quickly is not normally a good sign.
Thankfully it's often a simple fix, but that's still to be determined...

Good luck!

Paul

 

Sounds like a cracked distributor cap to me.

 

It's been replaced.

 

Open the computer and inspect for signs of burned components and/or leaking capacitors. You have spark to all cylinders so that means the computer is seeing the PIP signal. As you already found the computer appears to not be triggering cylinders 1,3,5. You may not find any bad components, but given your symptoms the output driver transistors for firing the odd numbered injectors may be bad.

 

Confirmed 1992 with EEC IV
Codes are 331 and than 33
I know it could only have two or three digit codes but that is what I got.
Oh yea and 331 does not exist.

Guess I'll pull the EEC IV tomorrow and check inside it and report back.
Thanks!

 

If you are good with a soldering iron or have a friend do it; it's not a bad operation to replace and leaking caps. Did mine a few years ago (my fuel pump would not shut off when I turned the key) . I used caps from various computer boards and a track was corroded and opened so I used a wire out of some Ethernet cable I had.

 

I haven't gotten it a apart yet but is this bad?

 

That isn't really the kind of thing we want to see, no. The innards are what counts though.

 

Well help oh guru of the EECIV these two caps are completely rusted off the board only hanging on with one leg. Any idea what they are for? Would they cause my strange fuel injector behavior?